雷达与目标之间的几何结构如图2.25所示。
The geometry isillustrated in two dimensions in Fig. 2.25.
Figure 2.25. 多普勒频移由目标与雷达相对速度的径向分量决定Doppler shift is determined by the radial component of relativevelocity between the target and radar.
当目标直接靠近或远离雷达时，多普勒频移的幅度最大。
The magnitude of theDoppler shift is maximum when the target is traveling directly toward or awayfrom the radar.
无论目标速度如何，当目标速度方向与雷达视线方向垂直交叉时，多普勒频移为零。
The Doppler shift iszero, regardless of the target velocity, when the target is crossingorthogonally to the radar boresight.
式（2.86）和（2.87）也可用于求解雷达目标其它运动模式的精确行为。
Equations (2.86) and(2.87) can be solved for the exact behavior of other regular patterns ofradar-target motion as well.
Gray和Addison（2003）的文献给出了恒加速度的求解。
The solution forconstant acceleration is given in Gray and Addison (2003).
即使在h(t)的闭式解很难或不可能找到的情况下，仍然可以使用迭代近似的方法来求解。
Even where a closedform solution for h(t) is difficult or impossible to find, it can still bedeveloped using an iterative approximation approach.
2.6.2. “停跳”近似与相位变化历史
2.6.2. The Stop-and-HopApproximation and Phase History
式（2.88）的准平稳假设提供了一个从相对于雷达运动的目标反射雷达脉冲的简化但非常有用的模型。
The quasi-stationaryassumption of Eq. (2.88) provides a simplified but very useful model ofreflection of a radar pulse from a target moving relative to the radar.
式（2.98）表明，接收回波的时间延迟与脉冲发射开始时的距离相对应，但相位调制与该距离内的时间变化有关。
Equation (2.98)states that the echo is received with a time delay corresponding to the rangeat the beginning of the pulse transmission but with a phase modulation relatedto the time variation in range.
这是雷达分析中常见的“停跳”假设中的“停”部分：回波包络看起来好像目标的运动在脉冲发射过程中停止了。
This is the"stop" part of the stop-and-hop assumption common in radar analysis:the envelope of the echo appears as if the target motion effectively stoppedwhile the pulse was in transit.
“跳”的部分也将很快讨论。
The "hop"portion will be discussed shortly.
式（2.98）不仅充分描述了恒定不变量，而且还充分描述了时变多普勒频移。
Equation (2.98)adequately describes not only constant but also time-varying Doppler frequencyshifts.
——本文译自Mark A. Richards所著的《Fundamentals of Radar Signal Processing（Second edition）》
更多精彩文章请关注微信号：